1. Field of the Invention
This invention relates to a process for selectively converting toluene or ethylbenzene to the para and meta ethyl derivatives thereof, utilizing a specified steam treated crystalline aluminosilicate zeolite catalyst.
2. Description of the Prior Art
Alkylation of aromatic hydrocarbons utilizing crystalline aluminosilicate catalysts has heretofore been described. U.S. Pat. No. 2,904,697 to Mattox refers to alkylation of aromatic hydrocarbons with an olefin in the presence of a crystalline metallic aluminosilicate having uniform pore openings of about 6 to 15 Angstrom units. U.S. Pat. No. 3,251,897 to Wise describes alkylation of aromatic hydrocarbons in the presence of X- or Y-type crystalline aluminosilicate zeolites, specifically such type zeolites wherein the cation is rare earth and/or hydrogen. U.S. Pat. Nos. 3,751,504 to Keown et al. and 3,751,506 to Burress describe vapor phase alkylation of aromatic hydrocarbons with olefins, e.g. benzene with ethylene, in the presence of a ZSM-5 type zeolite catalyst.
While the above-noted prior art is considered of interest in connection with the subject matter of the present invention, the selective ethylation process described herein utilizing a catalyst of a crystalline aluminosilicate zeolite, said zeolite having a silica/alumina ratio of at least about 12 and a constraint index of 1 to 12, which catalyst has undergone prior modification by treatment with steam to alter the activity and sorption characteristics thereof to achieve unexpectedly high selective production of the para and meta derivatives of a mono alkyl benzene, substantially free of ortho derivative thereof has not, insofar as is known, been heretofore described.
Both ethyltoluene and diethylbenzene are valuable chemicals. Thus, ethyltoluene may further be dehydrogenated to produce the corresponding vinyltoluene. The latter is used, to a large extent, in fiberglass-reinforced polyesters where the lower volatility of vinyltoluene and the reduced shrinkage in the final product make it superior over corresponding use of styrene. Vinyltoluene is also used to a lesser extent in alkyd paints where it has the advantage over styrene of a higher flash point and better film toughness. Copolymers of vinyltoluene with butadiene and with alpha-methylstyrene are used in adhesives, traffic paints, inks and hot melts where their principal advantage is rapid dry or cure time.
It has heretofore been recognized that the presence of substantial quantities of the ortho isomers is highly undesirable in the charge undergoing dehydrogenation since it tends to lead to ring closure with formation of the corresponding indenes and indanes which adversely affect the properties of the resultant polymer. The indenes and indanes so formed are difficult to separate from the desired vinyl aromatic products. It has accordingly heretofore been necessary to remove the ortho isomers from the ethyltoluene and diethylbenzene charge stocks by expensive distillation techniques prior to dehydrogenation thereof.
It is evident that the availability of ethyltoluene or diethylbenzene in which the ortho isomer is initially absent or present only in trace amount would eliminate the necessity for expensive prior removal of this isomer. Such products have, however, not heretofore been available.